There has been known a fuel supply device which is constituted of a fuel pump, a common rail which accumulates a high-pressure fuel supplied under pressure from the fuel pump, and fuel injection valves which are provided for respective cylinders of an internal combustion engine and are capable of supplying the high-pressure fuel accumulated in the common rail, and is referred to as a common rail system. In this type of the fuel supply device, as shown in FIG. 1 of JP-A-2001-263198, respective outlet ports of the fuel pump and the common rail are connected with each other by way of two high-pressure pipes which are provided independently from each other, and the high-pressure fuel from the respective outlet ports are supplied to the common rail by way of these two high-pressure pipes.
In this manner, the fuel pump which arranges high-pressure generating portions in a row adopts piping in which the fuel pump and the rail are connected with each other by a high-pressure pipe for every cylinder and hence, with respect to the fuel pump which is required to allow a large quantity of fuel to pass therethrough, a flow rate per hour that is allocated to one high-pressure generating portion becomes considerably large. Accordingly, due to throttling of an inner-diameter portion of the high-pressure pipe which is connected to the high-pressure outlet portion, the pressure is elevated at an outlet portion thus giving rise to a drawback with respect to the reliability of the high-pressure generating portion.
That is, in the conventional fuel supply device, a pressure resistance design having a sufficient margin with respect to an upper limit of the pressure fluctuation is usually performed by taking a lifetime of a product into consideration. However, in case that the pressure fluctuation of the fuel injected from the fuel pump is large, it is necessary to increase the pressure resistance value of the whole system including a fuel injection valve, a common rail, a pipe which connects the fuel pump and the common rail, a pipe which connects the common rail and the fuel injection valve and the like to a value which exceeds the necessary pressure resistance. Although it may be possible to suppress the elevation of pressure by increasing an inner diameter of the pipe, there may be a case that the sufficient inner diameter cannot be ensured due to the restriction imposed on strength, a mounting size and the like of the pipe. Further, when the pressure fluctuation is large, there arise drawbacks such as the increase of weight attributed to the increase of a wall thickness of constitutional parts and the complication of the structure attributed to the pressure resistance design.
It is an object of the present invention to provide a fuel supply device which can overcome the above-mentioned drawbacks of the related art.
It is also an object of the present invention to provide a fuel supply device which can suppress the elevation of pressure in the inside of a high-pressure pipe in comparison with a related art.
It is another object of the present invention to provide a fuel supply device which can realize the reduction of weight and the miniaturization thereof.